In the past, vehicles that moved through amusement park rides simply transported passengers through the ride, from scene to scene. In order to improve the experience of a rider, vehicles became more complex. In many of the newest vehicles, passengers are seated atop a motion base. The motion base enhances a rider's experience by changing the rider's orientation with respect to the vehicle as the vehicle carries the motion base (and passengers) through the amusement park ride.
With reference to a three dimensional coordinate system, having three orthogonal axes, one can describe the motion of a body (e.g., a platform atop a motion base) in three dimensional space by making reference to the number of “degrees of freedom” the body can experience. The six degrees of freedom most typically described are the three motions corresponding to translations of the body along the three orthogonal axes, and the three motions corresponding to the rotation of the body about the three orthogonal axes. Translations forward and backward may be referred to as surge. Translations upward and downward may be referred to as heave. Translations to the left and right may be referred to as sway. Rotation about the vertical axis may be referred to as yaw. Rotations about a longitudinal horizontal axis may be referred to as roll. Rotation about a transverse horizontal axis may be referred to as pitch. An airplane is useful example to describe the three motions corresponding to the rotations of the body (i.e., the airplane) about the three perpendicular axis. Changes in pitch are visually exemplified by the upward/downward tipping of the airplane's nose with respect to its tail. Changes in roll are visually exemplified by the left/right tipping of an aircraft's wingtip above or below the opposing wingtip. Changes in yaw are visually exemplified by clockwise/counterclockwise rotations of the airplane parallel to a horizontal plane, similar to the rotation of a compass needle with respect to the compass face. Everyday vehicles, such as automobiles, may experience less than all of the motions under normal operating conditions. Vehicles, such as airplanes, may experience all six motions, although the changes in motion may be so gentle that a passenger does not recognize that the changes are occurring.
For example, in the day-to-day experiences of passengers aboard a commercial aircraft, passengers are often unaware of (that is, they do not perceive of) the movement of the airplane relative to the Earth. Exceptions to this observation involve abrupt movements, such as a sudden change in altitude, or such as the immediate stop in vertical motion associated with a landing. The same unawareness is true of automobile passengers who, for example, may be unaware of the gradual banking (change in roll) of the automobile as the automobile speeds through a gradual turn on a highway. Humans may not tend to notice gradual changes in motion because these changes are not generally undesirable.
However, it appears to be a natural human instinct to notice, even subconsciously, a rapid change in motion. It is somehow self-evident to people that abrupt movements, for example in an airplane or in a ground transportation vehicle, are undesirable. These movements are typically associated with emergency situations, which may be life-threatening. In fact, human beings are born with what has been termed a “startle response” or a “startle reaction.” This much is apparent by observing any infant's response to a sharp movement, like an unexpected drop (e.g., a rapid heave), a sudden lurch forward, backward, or sideways, (e.g., rapid surge or sway), or a sudden change in orientation (e.g., a rapid roll or change in pitch). The human reaction is reflexive.
While undesirable in day to day life, it has been found, that abrupt movements are particularly desirable in many amusement park rides. Many of these rides may seek to elicit the startle response from the riders, whether by visual, auditory, or motion/movement stimuli. For example, it may be desirable to abruptly plunge the passengers in a ride vehicle downward by a precise amount of distance (i.e., negative heave) in order to help them experience a bus falling into a hole caused by an earthquake. By way of another example, the excitement of an escape of a vehicle from the jaws of a giant human-eating predator may be enhanced by a forceful and sudden tipping of a ride vehicle sideways (e.g., a sudden roll to right or left by a precise amount), in coordination of the change in yaw, and forward velocity of the vehicle. By way of still another example, avoidance of a vehicle replicating a submarine from an oncoming torpedo, or an airplane from an oncoming missile, may demand an immediate nose down dive (e.g., an abrupt negative change in pitch by a precise amount) coordinated with a drop (e.g., a negative heave). While scenery and visual illusions may have a part to play in simulating these movements, it is thought that providing the passenger with the true experience of movement in all six, or a subset of the six, degrees of freedom, is the most life-like and therefore the most exciting stimuli a rider can experience.